Objective Assess whether coronavirus disease 2019 (COVID-19) vaccination impacts menstrual bleeding quantity. Design Retrospective cohort Setting Five global regions Populations Vaccinated and unvaccinated regularly cycling individuals using the digital fertility-awareness application “Natural Cycles”. Methods We used prospectively collected menstrual cycle data and multivariable longitudinal Poisson GEE models, multivariable multinomial logistic regression models, and calculated the adjusted difference between vaccination groups. All regression models were adjusted for confounders. Outcome measures Mean number of heavy bleeding days (fewer, no change, more) and changes in bleeding quantity (less, no change, more) at three time points (first dose, second dose, and post-exposure menses). Results We included 9,555 individuals (7,401 vaccinated, 2,154 unvaccinated). About 2/3 of individuals reported no change in the number of heavy bleeding days regardless of vaccination status. After adjusting for confounders, there were no significant differences in the number of heavy bleeding days by vaccination status. A larger proportion of vaccinated individuals experienced an increase in total bleeding quantity (34.5% unvaccinated, 38.4% vaccinated; 4.0% [0.7, 7.2%] adjusted difference). This translates to an estimated 40 additional people per 1,000 normally cycling individuals who experience more total bleeding quantity following the first vaccine dose due to vaccination. Differences resolved in the cycle post-exposure. Conclusion A small increase in the probability of more total bleeding quantity occurs following the first COVID-19 vaccine dose which resolved the cycle post-vaccination cycle. Total number of heavy bleeding days did not differ by vaccination status. Our findings can reassure the public that any changes are small and transie

Objective: We compared prenatal care utilization, preterm birth, and low birth weight neonates among women 35 years and older compared to women 20-34 years old in Mexico, 2008-2019. Methods: We used birth certificate data and conducted a historical cohort study of all singleton live births in Mexico from 2008-2019. Study outcomes were inadequate prenatal care (timing of initiation of care and number of visits), preterm birth, and low birth weight. We compared outcomes among women 35-39, 40-44, and 45-49 with births to women 20-34. We used logistic regression to account for individual and contextual confounders. Results: We included a total of N=19,526,922 births; 11.9% (n=2,325,725) were to women 35 and older. Compared to women aged 20 to 34, the oldest (45-49 years old) were more likely to reside in poorer communities, have less education, and be uninsured. The odds of inadequate prenatal care (aOR 1.12 95% CI 1.09-1.15 p<0.01), preterm birth (aOR 2.05 95% CI 1.97-2.13 p<0.01), and low birth weight (2.03 95% CI 1.95-2.12 p<0.01) were highest for women 45-49, compared to women 20-34. Patterns were similar among women 35-39 and 40-44 with the exception of lower odds of inadequate prenatal care (aOR 0.77 95% CI 0.76-0.77 p<0.01) for 35-39 compared to women 20-34. Conclusion: Women who deliver at 35 years old and over are a heterogeneous group in Mexico. Being 35 years old and older is associated with increases in preterm birth and low birth weight neonates. Women who give birth between 45-49 may be especially vulnerable.